So what if your best share is higher than the difficulty and then the difficulty subsequently rises to a number that is higher than your best share? Did you still find a block?

Yes, because difficulty adjustments only happen when new blocks are solved. You solved a block at the current difficulty, then more blocks were solved and then the difficulty adjusted. It's not like the block you solved gets erased. If that were the case, then the vast majority of solved blocks would've been erased, and we wouldn't have a working blockchain.